Concentration of phosphate ores



P 1955 w. M. HOUSTON ETAL 5 CONCENTRATION OF PHOSPHATE ORES Filed Dec. 7, 1953 Phosphate Ore Feed Negative-ion reagents,such as caustic soda,fattyacid and fuel oil.

Conditionj g Froth Product Rougher Phosphate Concentrate Treatment Using Acid To retard Flotation RETARDED ELOTATION Phosphate Concentrate (2) Froth-Product Machine Discharge E* -"J M TREATMENT RESULTING IN AN INCREASE IN pH Silicious Machine-Discharge FINAL HIGH-GRADE PHOSPHATE CONCENTRATE INVENTORS Wesley M. Houston r AZ/omeys United States Patent CONCENTRATION OF PHOSPHATE ORES Wesley M. Houston and Harvie W. Breathitt, Jr., Lakeland, Fla, assignors to Minerals & Chemicals Corporation of America, a corporation of Maryland Application December 7, 1953, Serial No. 396,572 7 Claims. (Cl. 209-166) The present invention relates to the concentration of phosphate ores, and may be considered an improvement upon the method covered by a copending patent application, Serial No. 177,374, U. S. Patent No. 2,661,842 filed August 3, 1950, which is owned by the assignee of the present application.

The aforesaid application describes a method of concentrating phosphate minerals from their ores, which comprises (1) subjecting the ore in an aqueous pulp to a frothflotation treatment with negative-ion reagents, thereby producing a froth-product which is a rougher concentrate of the phosphate values mixed with some silicous gangue, and a silicious machine-discharge which is sent to waste; (2) subjecting said rougher concentrate in an aqueous pulp to retarded froth-flotation treatment and removing as a part of the final product a froth-product having a low insoluble content, and a middling machine-discharge; (3) subjecting said middling in an aqueous pulp to treatment with a mineral acid followed by rinsing with water, thereby removing from said middling substantially all of the negative-ion reagents; and (4) subjecting said acid-treated and rinsed middling in an aqueous pulp to a froth-flotation treatment with positive-ion reagents, thereby producing a froth-product mostly composed of silicious gangue which is discarded, and a residue which is a high-grade phosphate concentrate which is combined with the previously mentioned high-grade phosphate concentrate; thereby producing a final high-grade phosphate concentrate containing a high proportion of the phosphate in the ore.

The present invention is the result of our conception and discovery that the method described in the abovementioned application may be simplified and made more economical by modifying said method as hereinafter described, with the result that the use of mineral acid for de-oiling in step (3), and the use of positive-ion reagents in step (4), are eliminated.

The method of the present invention will be understood from the following description, taken in connection with the accompanying drawing which is a simplified general flow-sheet of a typical plant practicing the invention. In this drawing, the three steps of the method are separated by dash lines and are marked (1), (2) and (3). It will be understood, that this flow-sheet may be modified in many respects without departing from the spirit of the invention as defined in the claims hereto appended.

The steps of our improved method will now be described with the aid of the drawing.

The first step (1) in our improved method is the same as the first (1) step in the method described in the aforesaid copending application. That is, the phosphate ore feed is conditioned with suitable negative-ion reagents, such as caustic soda, fatty acid and fuel oil, and is then subjected to a rougher froth-flotation treatment which produces a froth-product which is a rougher phosphate concentrate, and a silicious machine-discharge which is sent to waste.

The second (2) step in our improved method is the same as the second (2) step in the method described in the aforesaid application. That is, the rougher phosphate concentrate from the first (1) step is subjected in step (2) to retarded froth-flotation treatment by the method described in the aforesaid application, wherein acid is added to the rougher concentrate pulp, with the result that the retarded froth-flotation treatment in step (2) produces a froth product which is a high-grade phosphate concen- 2,706,557 Patented Apr. 19, 1955 trate, and a machine-discharge which is a phosphate-rich middling.

In step (3) of our improved method, a pulp of the phosphate-rich middling produced in step (2) is subjected to a treatment resulting in an increase in the pH of said pulp. This treatment consists in adding to the said pulp an alkali, such as caustic soda, or a small quantity of negative-ion reagents such as those used in the first step (1); or the treatment may consist in merely adding tap water to the said pulp. After the pH of the pulp of the phosphate-rich middling has been thus increased, said pulp is subjected to negative-ion froth-flotation treatment which yields a froth-product which is a phosphate concentrate suitable for addition to the phosphate concentrate produced in step (2), and a silicious machine-discharge which is sent to waste.

From the foregoing description, it will be apparent that our improved method diflers from the method of the aforesaid copending application in that the phosphate-rich middling produced in step (2), instead of being de-oiled and subjected to flotation treatment with positive-ion reagents, is subjected to a treatment resulting in an increase of its pH, and is then subjected to a negative-ion flotation treatment yielding a froth-product which is a phosphate concentrate, and a silicious machine-discharge which is sent to waste. As shown in the drawing, the phosphate concentrate thus obtained in step (3) may be added to the phosphate concentrate produced in the second (2) step or otherwise disposed of. v

For a fuller understanding of preferred ways of practicing the method of our invention, attention is called to the following examples illustrating successful practicing of it. In each of the examples, the feed was obtained from the flotation feed to an operating phosphate concentrating plant. In Example I, the increase in the pH of the pulp of the phosphate-rich middling subjected to negative-ion flotation in step (3) was accomplished merely by the addition of tap water; in Example II said increase of pH was due to the addition of caustic soda; and in Example III said increase of pH was accomplished by the addition of small quantities of negative-ion reagents. In the examples three ways of adding acid to the pulp in step (2) are described.

Example I In step (1), the phosphate ore feed was conditioned for about two minutes in an aqueous pulp, containing approximately 70% solids, with 0.7 pound of caustic soda, 3.0 pounds of fuel oil and 0.7 pound of tall oil, all quantities being given in pounds per ton of dry feed. The conditioned feed was then diluted with tap water to about 20% solids in a Minerals Separation laboratory airflow flotation machine, and was then agitated and aerated to produce a silicious machine-discharge, and a froth-product which was a rougher phosphate concentrate in which a considerable amount of silicious material was entrained.

In step (2), the rougher phosphate concentrate was agitated for about two minutes in an aqueous pulp containing approximately 50% solids, and was then repulped in the flotation machine with tap water containing suflicient sulfuric acid to give it (the water) a pH of about 3.3. This rougher concentrate pulp was agitated and aerated to produce a froth-product which was a retarded phosphate concentrate of high grade, and a phosphate-rich middling machine discharge.

In step 3), a pulp of the phosphate-rich middling was returned to the flotation machine and its pH was increased by the addition of sufiicieut tap water to bring the pulp to flotation level; and then the said pulp was agitated and aerated to produce a phosphate concentrate froth-product and a silicious machine discharge.

Data pertinent to the pH aspect of this example was as follows: The amount of H2804 used in step (2) was 0.85 lb./ton of feed. The pH of rougher concentrate pulp in step (2) after the agitation at 50% solids was The pH of the pulp in the cell in step (2) at the end of the retarded float was 6.2. The pH of the pulp in the cell at the end of the final float (step 3) was 7.7.

Per- Per- Per- Percent Product cent cent cent BPL Wt. BPL Insol. IRecovery 1. Feed 100.0 27.2 100.0 2. Step (2) retarded phosphate concentrate 16. 9 76. 4 2. 3 47. 4 3. Step (3) concentrate 12.9 74.6 5.0 35.1 4. Step (3) silicious machine discharge 3. 43. 8 4. 9 5. Step (1) tailing 67.2 5.1 12.0

OVERALL RESULTS 6. Combined phosphate concentrates (Items 2 and 3) 29. 8 75. 0 3. 82. 5 7. Combined tailings (Items 4 and Thus from ore of 27.2% B. P. L. a phosphate concentrate of 75.6% B. P. L. and only 3.5% insoluble was obtained, said concentrate representing a recovery of 82.5% of the B. P. L. in the ore feed. These results were achieved without the addition of reagents, but merely tap water, in the last flotation step (3) of the method.' Obviously, the machine discharge from step (3) could be recirculated to the original feed and further increase recovery.

Example 11 In this example, the results were almost exactly the same as Example I through the retarded flotation step (2). The only differences were apparent and unintentional, being well within experimental error.

In step (3), the pH of the phosphate-rich middling pulp, in the flotation machine, was increased by the addition of caustic soda (NaOH); and then the pulp was agitated and aerated to produce in step (3) a phosphate froth-product and a silicious machine-discharge. Before and during this flotation operation tap water was added to keep the pulp at the flotation level.

The pH and related data were as follows: The amount of H2804 used in step (2) was 0.84 lb./ton of feed. The amount of caustic soda used in step (3) was 0.07 lb./ton of feed. The pH of rougher concentrate pulp in step (2) after the agitation at 50% solids was 8.1. The pH of the pulp in the cell at the end of the retarded float was 6.4. The pH of the pulp in the cell at the end of the final float (step 3) was 8.2.

The metallurgical results are in the table below:

Per- Per- Per- Percent Product cent cent cent BPL Wt. BPL Insol. Recovery 1. Feed 100.0 27.2 100.0 2. Step (2) retarded phosphate concentrate 21. 9 76. 4 2. 5 61. 3 3. Step (3) concentrate 9.2 72.6 7.2 24. 5 4. Step (3) silicious machine discharge 1.7 25. 3 1. 6 5. Step (1) tailing 67.2 5.1 12.6

OVERALL RESULTS 0. Combined phosphate concentrates (Items 2 and 3) 31.1 75. 3 3. 9 85. 8 7. Combined tailings (Items 4 and Thus from ore of 27.2% B. P. L. there was obtained a phosphate concentrate of 75.3% B. P. L. and only 3.9% insoluble, said concentrate representing a recovery of 85.8% of the B. P. L. in the ore. It will be noted that these results were achieved by using only a very small quantity of caustic soda in the final flotation step.

Example 111 In this example, step (1) was the same as in Examle I. p In step (2), the rougher concentrate produced in step (I) was agitated with H2504 for about 30 seconds, and then was pulped in the flotation machine with tap water to the proper level. This pulp was then agitated and aerated to produce a retarded phosphate concentrate of high grade and a phosphate-rich middling machine-discharge. The middling machine-discharge was removed from the cell and conditioned for about two minutes, in an aqueous pulp containing approximately 70% solids, with 0.10 lb. of caustic soda, 0.32 lb. of fuel oil and 0.06 lb. of tall oil, all quantities being given in pounds per ton of dry feed. The re-conditioned middling was then pulped in a Minerals Separation laboratory airflow flotation machine with tap water, agitated and aerated to produce in step (3) a phosphate froth-product and a silicious machine discharge.

The pH and related data were as follows: The amount of H2504 used in step (2) was 0.52 lb./ton of feed. The pH of the acid agitation pulp was 6.2. The pH of the pulp in the cell at the end of the retarded flotation (step 2) was 7.2. The pH of the conditioned middling pulp was 8.9 before diluting for flotation in step (3).

The metallurgical results are tabulated below:

Percent Wt.

Percent BPL Per- Percent cent BPL Insol. Recovery Product Step (2) retarded phosphate concentrate Step (3) concentrate Step (3) silicious machine dis charge Step (1) tailing 6 OVERALL RESULTS 0. Combined phosphate concentrates (Items 2 and 3) 7. Combined tailings (Items 4 and Step (1) of this example (rougher flotation) was the same as in Example I.

In step (2), the rougher phosphate concentrate was pulped in a Minerals Separation laboratory airflow flotation machine with tap water containing sufficient sulfuric acid to give it (the tap water) a pH of 3.6. The resulting pulp was agitated and aerated to produce a retarded phosphate concentrate of high grade and a phosphate-rich middling machine-discharge.

In step (3), the pH of the pulp of the phosphate-rich middling was increased by the addition of a small quantity of caustic soda, and then the pulp was agitated and aerated, after bringing it to the proper level with tap water, to produce a phosphate froth-product and a silicious machine-discharge.

The pH and related data were as follows: The amount of H2804 used was 0.76 lb./ton of feed. The amount of caustic soda used was 0.07 lb./ton of feed. The pH of the pulp in the cell at the end of the retarded float (step 2) was 6.3. The pH of the pulp in the cell at the end of the final flotation (step 3) was 8.3.

The metallurgical results are tabulated below:

Per- Per- Per- Percent Product cent cent cent BPL Wt. BPL Insol. Recovery 1. Feed 100.0 28.0 100.0 2. Step (2) retarded phosphate concentrate 19. 3 75. 9 2. 8 52. 3 3. Step (3) concentrate 12. 5 74.0 6. 2 33.1 4. Step (3) silicious machine discharge 2.3 28. 5 2. 3 5. Step (1) tailing 65.9 5.2 12.3

OVERALL RESULTS 6. Combined phosphate concentrates (Items 2 and 3) 31. 8 75.2 4. 2 85. 4 7. Combined tailings (Items 4 and In this example, the final product contained 75.2% B. P. L. and 4.2% insoluble, and the recovery was 85.4% of the B. P. L. in the feed.

What we claim is:

l. A method of concentrating phosphate minerals from their ores which includes the following steps: (1) subjecting the ore in an aqueous pulp to a froth-flotation treatment with negative-ion reagents, thereby producing a froth-product which phate values mixed with some silicious' gangue, and a tail ing consisting chiefly of silicious material which is discarded; (2) subjecting said rougher concentrate to retarded froth-flotation treatment in which the normal floatability of the phosphate is restrained by adding acid to the pulp, thereby producing a froth-product which is a phosphate concentrate having a low insoluble content, and a machine-discharge which is a phosphate-rich middling; and (3) refloating said phosphate-rich middling in a pulp having a higher pH than that of said middling, thereby producing a froth-product which is a concentrate of phos phate values which can be combined with the concentrate from step (2), and a tailing consisting chiefly of silicious material which can be discarded.

2. The method of claim 1 wherein approximately neutral water is added in step (3) to the phosphate-rich middling pulp to increase its pH prior to the final froth-flotation treatment.

is a rougher concentrate of the phos-- 3. The method of claim 1 wherein a small amount of caustic soda is added in step (3) to the phosphate-rich middling pulp to increase its pH prior to the final frothflotation treatment.

4. The method of claim 1 wherein small amounts of negative-ion reagents are added in step (3) to the phosphate-rich middling pulp to increase its pH prior to the final froth-flotation treatment.

5. The process of claim 1 wherein the step (2) retarded flotation treatment is efiected by carrying out the flotation operation using weakly acid flotation water.

6. The process of claim 1 wherein the step (2) retarded flotation treatment is effected by agitating an aqueous pulp of the rougher concentrate for a relatively short while and then subjecting it to froth flotation treatment in weakly acid flotation water.

7. The process of claim 1 wherein the step (2) retarded flotation treatment is eflected by agitating a weakly acid pulp of the rougher concentrate for a short period of time and then subjecting it to froth flotation treatment using approximately neutral water for pulp dilution.

Duke et al. Apr. 27, 1954 Hodges et a1 June 29, 1954 

1. A METHOD OF CONCENTRATING PHOSPHATE MINERALS FROM THEIR ORES WHICH INCLUDES THE FOLLOWING STEPS: (1) SUBJECTING THE ORE IN AN AQUEOUS PULP TO A FROTH-FLOTATION TREATMENT WITH NEGATIVE-ION REAGENTS, THEREBY PRODUCING A FROTH-PRODUCT WHICH IS A ROUGHER CONCENTRATE OF THE PHOSPHATE VALUES MIXED WITH SOME SILICIOUS GANGUE, AND A TAILING CONSISTING CHIEFLY OF SILICIOUS MATERIAL WHICH IS DISCARDED; (2) SUBJECTING SAID ROUGHER CONCENTRATE TO RETARDED FROTH-FLOTATION TREATMENT IN WHICH THE NORMAL FLOATABILITY OF THE PHOSPHATE IS RESTRAINED BY ADDING ACID TO THE PULP, THEREBY PRODUCING A FROTH-PRODUCT WHICH IS A PHOSPHATE CONCENTRATE HAVING A LOW INSOLUBLE CONTENT, AND A MACHINE-DISCHARGE WHICH IS A PHOSPHATE-RICH MIDDLING; AND (3) REFLOATING SAID PHOSPHATE-RICH MIDDLING IN A PULP HAVING A HIGHER PH THAN THAT OF SAID MIDDLING. THEREBY PRODUCING A FROTH-PRODUCT WHICH IS A CONCENTRATE OF PHOSPHATE VALUES WHICH CAN BE COMBINED WITH THE CONCENTRATE FROM STEP (2), AND A TAILING CONSISTING CHIEFLY FO SILICIOUS MATERIAL WHICH CAN BE DISCARDED. 